Remember the Feast of the Holy Innocents? The Church has always remembered the infants slaughtered by Herod as something akin to martyrs. They had no say in the matter, but they are still honored and remembered.
Yes, the Church teaches that the normal means of salvation is by baptism and membership in the Catholic Church. Jesus clearly gave us that path, and we who know the path are required to follow it.
However, Dominus Iesus clearly refutes the assumption that anyone not baptised or not Catholic is therefore damned to Hell. We do not know, it said, how God deals with those who were never evangelized, were raised in a rabidly anti-Catholic home, or died before they could be baptised. We hope on God’s mercy.
Limbo for unbaptised children is not a 2,000 year old idea. “The Limbo of the Fathers” tried to explain what happened to the Saints of the OT before Jesus’ Resurrection and the subsequent opening of Heaven. Limbo for babies was more of a Middle Ages idea. Parents understood that baptism was necessary for salvation, but couldn’t accept the idea that their child that died suddenly at two days old was going to hell. If God was really merciful and just, where were the mercy or justice for this child? Limbo for babies tried to reconcile the two ideas: the baby wouldn’t go to Heaven, but would be perfectly naturally happy, as Adam and Eve were before the Fall.
But if only Heaven is the fulfillment we seek, then even Limbo would be something of a punishment, wouldn’t it?